The present invention relates to a video disk recorder and playback unit.
Disks capable of recording data of high density have recently been developed and commercialized. Video disks and digital audio disks (compact disks) are typical examples.
The optical video disk has spectrum characteristics as shown in FIG. 1. Television video signals, whose synch pulse and white levels are at 7.6 MHz and 9.3 MHz, respectively, are recorded using frequency modulation, and two accompanying audio signals, such as left- and right-channel stereo signals or bilingual signals, having carriers at 2.3 MHz and 2.8 MHz, are also recorded using frequency modulation.
In the case of an optical digital audio disk, the spectrum of the EFM signals of the left and right stereo audio signals, which are in CPM form, occupies a frequency band lower than about 2 MHz, as shown in FIG. 2. As the above-described band of lower than 2 MHz is left substantially unoccupied on a video disk, such EFM signals can be recorded on the video disk in that band using a frequency-division multiplexing method. FIG. 3 illustrates the spectrum in that case. It can be seen from FIG. 3 that in this case all signals can be separated satisfactorily.
FIG. 4 is a block diagram of a video disk recorder which records signals in the above-discussed format. In the recorder, the high frequency component, pre-emphasized by a pre-emphasis circuit 1, of a television video signal is modulated by an FM modulator 2 and applied to one input of an adder 3. Audi signals in two channels are pre-emphasized in pre-emphasis circuits 4 and 5 and are frequency modulated by respective FM modulators 6 and 7 before being applied to the adder 3. Moreover, the audio signals in the two channels are converted into digital values (PCM) by a PCM encoder, subjected to EFM modulation by an EFM encoder 9, unwanted high frequency components are removed by a low-pass filter 10, and then the signals thus processed are applied to the adder 3 through a pre-emphasis circuit 11. Accordingly, FM signals including the video signal, the FM signals of the audio signals in the two channels, and the EFM signals of the audio signals in the two channels are summed together by the adder 3, whereby a multiplex signal is produced. The multiplex signal is passed through a limiter 12 before being supplied to an optical modulator 13. Consequently, a laser beam produced by a laser source 14 is modulated according to the multiplex signal and irradiated onto a recording master disk 17, rotated by a motor 16, through an objective lens 15, so that the multiplex signal is recorded. Disk copies can then be made from the master disk 17 in a well-known manner.
FIG. 5 is a block diagram of a playback unit for playing back a disk thus prepared. A laser beam emitted from a pickup 23 is irradiated onto a disk 22, driven by a motor 21, through an objective lens 24, and light reflected from the disk is received by the pickup 23 through the objective lens 24 to thus generate a playback signal. The playback signal is passed through an amplifier 25, and the video signal from the amplified signal is supplied to an FM democulator 27 through a bandpass filter 26 for demodulation before being outputted through a de-emphasis circuit 28. The two audio signals are respectively supplied to FM demodulators 31 and 32 through bandpass filters 29 and 30 for demodulation. The corresponding demodulated signals are applied through deemphasis circuits 33 and 34 to an output amplifier. The EFM signal components are separated from each other by a low-pass filter 35 then supplied to an EFM decoder 37 and a PCM decoder 38 through a de-emphasis circuit 36 for EFM and PCM demodulation, and regenerated as analog signals. As a result, the user is allowed to select higher-fidelity audio signals from the output of the PCM decoder 38 in place of the normal signals provided through the FM demodulator 31.
Digital data signals may be recorded in place of the EFM audio signals. However, since a digital data signal is different in many ways from an audio signal, for instance, a digital data signal need not always be continuous, it is generally advantageous to record the former in blocks. In that case, whether or not the player remains simple in construction is dependent upon the selection of the relationship between the blocks and the corresponding video signal in terms of position on the disk.